"I guess I will join you." Mary held Faye's offered hand tenderly.
"Great, let's get you started." Faye led Mary into the bedroom. "What would you like? No wait, I think we should start you off with something a bit slow to get you ready." Faye plucked up a few vials and began mixing them together.
"What are you mixing?"
"Something to give a bit more shape to that washboard butt."
"Now that is just mean."
"Well you gotta admit, you don't leave much to be desired." Faye smirked and passed her the mixture.
Mary felt her face heat up from embarrassment. Her absolutely flat rear and negligible hips were one of her sore spots she hated about her body. "I guess this is my chance to change all that huh." Mary downed the mixture and passed the beaker back to Faye.
Mary didn't have to wait long before she felt a warmth in her rear. Soon it spread to her entire pelvis and legs. Mary gasped as her skin was pulled taut and then stretched even further. Mary walked over to the bedroom mirror and turned so she could see the changes. Despite her past experiences with the vials and her current height of nearly 8' tall, Mary still was awestruck as her originally flat and nondescript butt cheeks began to round out and swell. Mary grabbed one of the inflating cheeks and gasped as what felt like electricity surge through her.
"Fuck that feels good!" Mary excitedly watched as her hand was forced further and further back as the flesh piled on. But it wasn't the only part swelling. Mary had to shift her balance as her hips started to flare outwards, giving her a nice set of motherly hips to go with a perky rear that resembled a pair of soccer balls in size.
"Wow! That was great, what did you mix- OH!" Mary was cut off mid sentence as the heat focused on her crotch and thighs next. Mary rubbed her tingling pussy and found her mound was also swelling.
"What did you do?!" Mary wanted to glare angrily at her sister, but the pleasure was overwhelming. Mary's thighs expanded, causing them to sandwich her now engorged vagina.
"I thought you should feel about as good as I feel with this monster. And judging by your expression, you are loving this." Faye grinned, her hands moving towards her member and caressing the length idly.
"Oh fuck this feels great." Mary slid one finger between her pussy's engorging lips and began to stroke. As her lips swelled, she used 2 and then finally 3 fingers were used to pleasure herself. Finally Mary couldn't take it anymore and screamed as she was rocked by the most mind bending orgasm she had ever felt.
As she came down from her euphoria, Mary gasped when she realized she masturbated infront of her sister. Faye meanwhile was slowly stroking her equine member.
"Faye what are you doing?"
"Huh? Oh I was uh.... I gotta go take care of something. Be right back, try something new." Faye fled the bedroom and Mary heard another door shut.
With Faye gone, Mary took stock of her changes. Huge child bearing hips wider than her shoulders, an ass the size of a pair of volleyballs, thick thighs that were soft but still toned, and a vagina that looked swollen and wanting to be stuffed.
With Faye gone, Mary studied the options before her and wondered what possibilities lay before her.